Chromatography is one of the oldest chemical analysis methods in which a mixture is separated into individual chemical components. It thus becomes simpler to make a qualitative and quantitative determination of the chemical components in a mixture. In gas chromatography the mixture is guided through a separation column by means of an inert carrier gas: the mobile phase. The separation is based on the differential interactions between the different chemical components in the mobile phase and an immobilized stationary phase: a liquid or solid material with which the inner wall of the separation column is covered or which is arranged on an inert carrier material in the separation column. The retention time of a chemical component in the separation column is a function of the measure of interaction with the stationary phase, the type and the quantity of stationary phase, the length and diameter of the separation column, the type of carrier gas, the flow speed and the temperature. The different chemical components will in principle now leave the separation column at different points in time. These points in time can be determined by guiding the outflow from the separation column to a detector. The different chemical components then appear as more or less sharp ‘peaks’ in the output of the detector: the chromatogram.
Use is generally made in gas chromatography of a capillary separation column: a thin tube with an internal diameter normally varying from about 0.1 to 0.5 mm and a length normally varying from about 1 to 150 meters. Most capillary separation columns are made of fused silica with a protective layer of polyimide on the outside, although metal capillary separation columns are for instance also known. A very good separation with a high precision and reproducibility can be achieved using such capillary separation columns. In respect of its great length, a capillary separation column is generally at least partially coiled for the purpose of use. It must be possible to heat the capillary separation column, wherein it must be possible to regulate the temperature very precisely and preferably very quickly. For this purpose the coiled capillary separation column is generally placed in a heating oven, the temperature of which can be regulated very precisely. The capillary separation column can thus be brought uniformly and very precisely to a determined desired temperature. Varying of the temperature can however take place only relatively slowly because the thermal mass of the heating oven is relatively large.
For several decades there have also been miniaturized gas chromatographs which are manufactured making use of microstructural technology, wherein the separation column is etched in a suitable material, for instance WO 2006/042727 or WO 2004/065955. Dead volumes can be minimized by miniaturization and integration of the etched separation column, injector and detector. The cost price of the whole system can be lower. The dimensions, the weight and the energy consumption of such microsystems are further relatively small, whereby they can be given a portable form and utilized more flexibly on location. The required heating elements can herein be manufactured in integrated manner and the temperature of the etched separation column can be regulated relatively quickly because of the relatively small thermal masses. It has been found in practice however that the separating properties, precision and reproducibility of such etched separation columns still leave much to be desired. It has moreover been found difficult to heat an etched separation column uniformly since undesirable temperature gradients which are difficult to control readily occur.
DE 19707114 describes a system for capillary chromatography wherein a capillary separation column lies against the inner wall of a heating oven and is heated by means of a heating lamp placed in the oven. The advantage is that the capillary separation column can be heated relatively quickly. The system is however not suitable or hardly so, for manufacture by means of microstructural technology and miniaturization. US 2006/0283324 describes a capillary separation column encapsulated and adhered between two thin layers of fibreglass cloth. The whole is preferably attached by means of spacers to a base surface, for instance a printed circuit board, on which the heating is also arranged. Such a construction has the advantages that it is compact, that the capillary separation column can be heated relatively quickly and that use can be made of a usual capillary separation column with its very good separating properties, high precision and reproducibility. Drawbacks are however, among others, the complexity of the whole, the high cost price of manufacture by means of less usual technology and the undesired temperature gradients which occur.
There therefore exists a need for a system for capillary chromatography which has as far as possible both the advantages of miniaturized and integrated gas chromatographs and the advantages of the use of a more usual capillary separation column, wherein the capillary separation column can be heated uniformly, rapidly and accurately. The invention has for its object to fulfil this need.